Image of Lacaille 8760 (circled) in
Bode's Uranographia (1801).[1] In the corresponding catalog this star is listed as № 36 in constellation Microscopium.[2]
Location of Lacaille 8760 in the constellation
Microscopium
Lacaille 8760 (AX Microscopii) is a
red dwarf star in the
constellationMicroscopium. It is one of the
nearest stars to the Sun at about 12.9
light-years' distance, and the brightest
M-classmain-sequence star in Earth's night sky, although it is generally too faint to be seen without a
telescope. At an
apparent magnitude of +6.7, it may only be visible to the unaided eye under exceptionally good viewing conditions, under dark skies.
This star was originally listed in a 1763 catalog that was published posthumously by the
French Abbé
Nicolas-Louis de Lacaille. He observed it in the southern sky while working from an observatory at the
Cape of Good Hope.[14] Number 8760 was assigned to this star in the 1847 edition of Lacaille's catalogue of 9,766 stars by
Francis Baily.[15]
In the past, Lacaille 8760 has been classified anywhere from spectral class
K7 down to
M2. In 1979, the
Irish astronomer Patrick Byrne discovered that it is a
flare star,[16] and it was given the
variable star designation AX Microscopii, or AX Mic. As a flare star it is relatively quiescent.
Lacaille 8760 is one of the largest and brightest red dwarfs known, with about 60%[4] the mass and 51%[8] the radius of the Sun. It is about five[13] billion years old and is spinning at a
projected rotational velocity of 3.3 km/s,[6] giving it a
rotation period of roughly 40 days.[12] The star is radiating 7.2%[9] of the luminosity of the Sun from its
photosphere at an
effective temperature of 3,800 K.[10]
Despite efforts by astronomers, as of 2011 no planets had been detected in orbit around this star.[17]
Lacaille 8760 orbits around the galaxy with a relatively high
ellipticity of 0.23.[18] Its closest approach to the Sun occurred about 20,000 years ago when it came within 12 light-years (3.7
parsecs).[19] Due to its low mass (60% of the Sun), it has an expected lifespan of about 75 billion (7.5 × 1010) years,[20] seven times longer than the Sun's.
^
abByrne, P. B.; Doyle, J. G. (January 1989), "Activity in late-type dwarfs. III - Chromospheric and transition region line fluxes for two dM stars", Astronomy and Astrophysics, 208 (1–2): 159–165,
Bibcode:
1989A&A...208..159B.
^Allen, C.; Herrera, M. A. (April 1998), "The Galactic Orbits of Nearby UV Ceti Stars", Revista Mexicana de Astronomía y Astrofísica, 34: 37–46,
Bibcode:
1998RMxAA..34...37A.
^Despain, K. H. (December 1981), "Low-mass evolution - Zero-age main sequence to asymptotic giant branch", Astrophysical Journal, Part 1, 251: 639–653,
Bibcode:
1981ApJ...251..639D,
doi:10.1086/159510.